CODEWITHSUNDEEP
gccpositionfpic
Setjmp
Setjmp

Reputation: 28372

Is there a way to determine that a .a or .so library has been compiled as position indepenent code?

I am getting a linking error when compiling the numpy library against lapack indicating I need to compile lapack with -fPIC. I thought I had done just that. Is there a way to determine that the produced lapack library is position independent?

Upvotes: 23

Views: 11877

Answers (2)

user3141592653589
user3141592653589

Reputation:

You may have some luck with this answer, although it's platform dependent and doesn't work for all object files (but if you code manipulates pointers in any way, it should work).

This is the result of objdump -r on a file compiled with -fPIC: 

test.o:     file format elf32-i386

RELOCATION RECORDS FOR [.text]:
OFFSET   TYPE              VALUE 
00000007 R_386_PC32        __i686.get_pc_thunk.cx
0000000d R_386_GOTPC       _GLOBAL_OFFSET_TABLE_

and this is for a file without PIC:

test.o:     file format elf32-i386

Upvotes: 22

F'x
F'x

Reputation: 12298

In general, you have no way of knowing:

$ cat a.c
int foo(int x) { return x+1; }
$ gcc -fno-pic a.c -c -o nopic.o
$ gcc -fPIC a.c -c -o pic.o   
$ cmp pic.o nopic.o 
$ cmp pic.o nopic.o && echo Identical
Identical

Upvotes: -3

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